FinFET structure and method of manufacturing the same

ABSTRACT

A semiconductor structure and a method for forming the same are provided. The method includes providing a substrate, forming a fin structure extruding from the substrate, forming shallow trench isolations over the substrate, and forming an oxide material over the fin structure. The method further includes forming a carbon-doped amorphous silicon layer or a carbon-doped poly silicon layer over the oxide material, wherein the forming a carbon-doped amorphous silicon layer or a carbon-doped poly silicon layer includes doping carbon in a range of from about 5E19/cm 3  to about 1E22/cm 3 .

FIELD

The disclosure relates to a FinFET structure and a method ofmanufacturing the FinFET structure.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,a three dimensional transistor, such as a FinFET, has been introduced toreplace a planar transistor. Although existing FinFET devices andmethods of fabricating FinFET devices have been generally adequate fortheir intended purposes, they have not been entirely satisfactory in allrespects. For example, an irregular interface between a gate oxide and ametal gate of a FinFET raises challenges in a FinFET processdevelopment. It is desired to have improvements in this area.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion

FIG. 1A is a cross sectional view of a conventional Fin Field EffectTransistor (FinFET) structure after an anneal operation greater than 700degrees Celsius;

FIG. 1B is an enlarged cross sectional view of a conventional Fin FieldEffect Transistor (FinFET) structure after an anneal operation greaterthan 700 degrees Celsius;

FIG. 2 is a flow chart of forming a FinFET structure in accordance withsome embodiments of the present disclosure;

FIGS. 3A-3E show fragmental cross sectional views of various operationsfor manufacturing a FinFET structure in accordance with some embodimentsof the present disclosure;

FIG. 3F is a cross sectional view of conventional polysilicon gate afteran anneal operation;

FIG. 3G is a cross sectional view of an in-situ carbon-doped polysilicongate after an anneal operation, in accordance with some embodiments ofthe present disclosure;

FIG. 4A shows a cross sectional view of a non-annealed amorphous siliconbefore an etching operation;

FIG. 4B shows a cross sectional view of a non-annealed amorphous siliconafter an etching operation;

FIG. 4C shows a cross sectional view of polysilicon (annealed amorphoussilicon) before an etching operation;

FIG. 4D shows a cross sectional view of polysilicon (annealed amorphoussilicon) after an etching operation;

FIG. 5 is a flow chart of forming a FinFET structure in accordance withsome embodiments of the present disclosure;

FIGS. 6A-6D show fragmental cross sectional views of various operationsfor manufacturing a FinFET structure in accordance with some embodimentsof the present disclosure;

FIG. 6E is a cross sectional view of an in-situ carbon-doped polysilicongate after an anneal operation, in accordance with some embodiments ofthe present disclosure;

FIG. 6F is a cross sectional view of an ex-situ carbon-doped silicongate before an implant operation, in accordance with some embodiments ofthe present disclosure;

FIG. 6G is a cross sectional view of an ex-situ carbon-doped polysilicongate after an implant operation, in accordance with some embodiments ofthe present disclosure;

FIG. 6H is a cross sectional view of an ex-situ carbon-doped polysilicongate after an anneal operation, in accordance with some embodiments ofthe present disclosure;

FIG. 7 represents the normalized poly grain size with respect to variousthermal anneal conditions;

FIG. 8A is a FinFET structure with a metal gate in accordance with someembodiments of the present disclosure;

FIG. 8B is a cross sectional view of an interface between a gate oxideand a metal gate of a FinFET structure.

DETAILED DESCRIPTION OF THE INVENTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The making and using of the embodiments are discussed in detail below.It should be appreciated, however, that the present invention providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative of specific ways to make and use the invention, anddo not limit the scope of the invention.

In the conventional operation of manufacturing a FinFET device, anun-doped silicon layer is formed after forming a gate oxide on a gate ofa FinFET device. The un-doped silicon layer is formed under a lowertemperature (e.g. about 530 degrees Celsius) compared to some operationssubsequent to forming the un-doped silicon layer. However, during theoperation with higher temperatures, grains with different orientationsare formed at various locations in the silicon layer including at aninterface between the gate oxide and the un-doped silicon layer of theFinFET structure. The un-doped silicon layer is prone to recrystallizeunder a temperature higher than about 700 degrees Celsius. The volume ofthe recrystallized un-doped silicon layer is greater than that of thesilicon layer without recrystallization. Said volume expansion generatesgreater roughness at the interface between the gate oxide and thesilicon layer, and said roughness carries to the final product betweenthe gate oxide and the metal gate. The volume expansion of therecrystallized silicon layer also deteriorates the dimension uniformityof the metal gate, and thus impacts the performance thereof.Furthermore, the roughness between the metal gate and gate oxide leadsto greater leakage current in the FinFET device with metal gate.

FIG. 1A shows a cross section of a plurality of fins 100 after anannealing operation. The recrystallized a poly silicon layer 101 isformed over gate oxide 102 of a fin 100. FIG. 1B is an enlarged crosssection of the interface 103 between the gate oxide 102 and thepolysilicon layer 101 after the polysilicon layer 101 recrystallized.The shape of the interface 103 between the gate oxide 102 and thepolysilicon layer 101 is irregular. In some embodiments, the roughnessof the interface 103 between the gate oxide 102 and the polysiliconlayer 101 may impact the performance of a FinFET.

For reducing the recrystallization of the silicon layer, a flow chart ofa method 200 of introducing a carbon-doped silicon layer in the processof forming a FinFET device is shown in FIG. 2. The method 200 includes anumber of operations. Referring to FIG. 2 to FIG. 3E, in operation 201,a substrate 301 is provided as in FIG. 3A. In some embodiments, thesubstrate comprises silicon. In operation 202, a plurality of stripes302 are formed on the substrate 301 as shown in FIG. 3B. The material ofthe plurality of stripes 302 are usually the same as that of thesubstrate 301. FIG. 3C is a cross-sectional view illustrating in detailthe FinFET structure 300 of FIG. 3B, wherein the exemplarycross-sectional view is obtained by dissecting line A-A′ in FIG. 3B. TheFinFET structure 300 includes a substrate 301 and a plurality of stripes302. Isolations 306 are formed over the substrate 301, as shown in FIG.3C. In operation 203, an oxide material 303 is formed over the pluralityof stripes 302 and the isolations 306, as shown in FIG. 3D.

In operation 204, a silicon layer 304 is formed over the oxide material303 at a first temperature as shown in FIG. 3E. The silicon layer 304 isdeposited over the stripes 302. During the formation of the siliconlayer 304, the silicon layer 304 is implanted with carbon at aconcentration of from about 5E19/cm³ to about 1E22/cm³. In someembodiments, the silicon layer 304 is formed under a first temperaturefrom about 450 degrees Celsius to about 650 degrees Celsius, typicallyfrom 480 degrees Celsius to 620 degrees Celsius. In some embodiments,the silicon layer 304 is formed under a pressure from about 0.2 torr toabout 5.0 torr. Gases comprising SiH₄, C₂H₄ or H₂ are also introducedduring the formation of the silicon layer 304. The doping operation ofthe silicon layer being formed concurrently with dopant gas introductionis called in-situ doping operation in the present disclosure.

In operation 205, the temperature is elevated to a second temperaturegreater than the first temperature. For example, the operation forming alightly-doped drain (LDD) in the stripes 302 is usually processed at atemperature greater than about 700 degrees Celsius; and the source/drainannealing is usually processed at a temperature greater than about 1100degrees Celsius. Under such high temperatures, un-doped silicon layerwill recrystallize at various locations including at the interfaces 305a and 305 b between the gate oxide material 303 and the silicon layer304.

FIG. 3F is a cross sectional view of the interfaces 305 a and/or 305 bwithin the dotted lines in FIG. 3E. FIG. 3F shows a conventionalpolysilicon gate without carbon doping after an annealing operation. Therecrystallized silicon grains are formed at the interfaces 305 a and/or305 b between the gate oxide 303 and the silicon layer 304. FIG. 3Gshows a cross sectional view of an in-situ carbon-doped polysilicon gateafter an anneal operation, in accordance with some embodiments of thepresent disclosure. The recrystallized grains of the carbon-dopedsilicon are much smaller than those of the conventional non-carbon-dopedsilicon layer as shown in FIG. 3F.

During an annealing operation subsequent to the formation of the siliconlayer 304 over the gate oxide 303, polysilicon grains having differentsizes and different orientations may be formed at random locationsincluding the interfaces 305 a and/or 305 b between the gate oxide 303and the silicon layer 304. In some embodiments, the polysilicon grainsmay include orientations of <100>, <110> and <111>. FIG. 3F shows amicrostructure after an annealing operation at the interfaces 305 aand/or 305 b between the gate oxide 303 and the silicon layer 304enclosed by the dotted lines in FIG. 3E. The sizes and orientations ofgrains shown in FIG. 3F can be different. In some embodiments, thepolysilicon grains shown in FIG. 3F include an orientation of <111>.FIG. 3G shows a microstructure after an annealing operation at theinterfaces 305 a and/or 305 b between the gate oxide 303 and the siliconlayer 304 enclosed by the dotted lines in FIG. 3E. In some embodiments,the polysilicon grains shown in FIG. 3G include an orientation of <111>.It is understood that the grain size of the in-situ carbon-doped siliconlayer is generally smaller than the grain size of the silicon layerwithout carbon doping, therefore, the <111> grain in the in-situcarbon-doped silicon layer is generally smaller than the <111> grain inthe silicon layer without carbon doping. Hence, the <111> grain sizeformed at the interfaces 305 a and/or 305 b between the gate oxide 303and the in-situ carbon-doped silicon layer 304 can be reduced byintroducing carbon impurities into the silicon layer 304. In someembodiments, an average <111> grain size in the in-situ carbon-dopedsilicon layer about 0.02-0.07 μm.

Because the crystal structures of the grains are different, the grainsof different orientations may have different resistant to differentkinds of etchants. In some embodiments, the grains of the recrystallizedsilicon include at least the orientations of <100>, <110> and <111>. Toremove the grains at the interfaces 305 a and/or 305 b between the gateoxide 303 and the silicon layer 304, one or more etchants can beapplied. In some embodiments, the etchant may include Ammonium Hydroxide(NH₄OH). In some embodiments, under a wet etching with etchant NH₄OH:H₂O(3.7 wt % of NH₄OH) and an etching temperature of 40 degrees Celsius,the relative etching rates of polysilicon grains of orientations <100>,<110> and <111> are respectively 100, 37 and 3. After the etchingoperation, grains with orientation <111> may remain while grains withorientations <100>, <110> being removed. The remained <111> grains maycause great roughness between the metal gate and the gate oxide. Thismay lead to greater leakage current in the FinFET device with metal gateand cause the yield of the FinFET device to be unacceptable. By adoptingthe in-situ carbon-doped silicon layer as previously discussed, anaverage grain size of the <111> poly silicon is effectively decreased tobe lower than a predetermined value, and thus the small <111> grains areprone to be removed compared to the large <111> grains as a result of nocarbon doping

Now referring to FIGS. 4A-4D. FIG. 4A shows a cross sectional view of anon-annealed amorphous silicon before an etching operation. An amorphoussilicon layer 401 is sandwiched by an upper coating 402 and a lowercoating 405. FIG. 4B shows a cross sectional view of a non-annealedamorphous silicon after an etching operation. After etching, theamorphous silicon layer 401 sandwiched by the upper coating 402 and thelower coating 405 in FIG. 4B is obviously thinner than that in FIG. 4A.The upper interface 406 between the amorphous silicon layer 401 and theupper coating 402 is still smooth. FIG. 4C shows a cross sectional viewof polysilicon (annealed amorphous silicon) before an etching operation.After the anneal operation, polysilicon grains 403 are formed in theamorphous silicon layer 401. FIG. 4D shows a cross sectional view ofpolysilicon (annealed amorphous silicon) after an etching operation.Polysilicon grains 404 having different sizes may be formed. The etchingoperation is a wet etching with etchant NH₄OH:H₂O (volume ratio 5:1)under an etching temperature of about 50 degrees Celsius. After theetching operation, due to the incomplete removal of the <111> grains,the upper interface 406 between the amorphous silicon layer 401 and theupper coating 402 is rougher compared to the interface 406 as shown inFIG. 4B.

FIG. 5 shows a flow chart of a method 500 of forming a carbon-dopedamorphous silicon layer or a carbon-doped polysilicon layer in theprocess of forming a FinFET device. The method 500 includes a number ofoperations. Referring to FIG. 5 to FIG. 6D, in operation 501, asubstrate 601 is provided as in FIG. 6A. In some embodiments, thesubstrate comprises silicon. In operation 502, a fin structure extrudingfrom the substrate 601 is formed as shown in FIG. 6B. In someembodiments, material of the fin structure 602 can be the same as thatof the substrate 601. In operation 503, isolation structures such as ashallow trench isolation are formed over the substrate 601 as shown inFIG. 6C. FIG. 6C is a cross-sectional view illustrating in detail theFinFET structure 600 of FIG. 6B, wherein the exemplary cross-sectionalview is obtained by dissecting along line B-B′ in FIG. 6B. The FinFETstructure 600 includes a substrate 601 and a fin structure 602.Isolations 606 are formed over the substrate 601, as shown in FIG. 6C.In operation 504, an oxide material 603 is formed over a top surface 602a and a sidewall 602 b of the fin structure 602, as shown in FIG. 6D.

In operation 505, a carbon-doped silicon layer 604 is formed over theoxide material 603 and the stripes 602 as shown in FIG. 6E. Nowreferring to FIGS. 6A-6E. In some embodiments, the carbon-doped siliconlayer 604 may be a carbon-doped amorphous silicon layer or acarbon-doped polysilicon layer. The carbon-doped poly silicon layer canbe transformed from the carbon-doped amorphous silicon layer under atemperature greater than about 700 degrees Celsius in a subsequent hightemperature operation. During the formation of the carbon-doped siliconlayer 604, the carbon-doped silicon layer 604 is implanted with carbonatoms at a concentration of from about 5E19/cm³ to about 1E22/cm³. Ifthe concentration of the carbon atoms increases, the carbon atoms willbe more uniformly doped in the silicon layer.

In some embodiments, the carbon-doped silicon layer 604 is formed undera first temperature from about 450 degrees Celsius to about 650 degreesCelsius, typically from 480 degrees Celsius to 620 degrees Celsius. Insome embodiments, the carbon-doped silicon layer 604 is formed under apressure from about 0.2 torr to about 5.0 torr. Gases comprising SiH₄,C₂H₄ or H₂ are also introduced during the formation of the carbon-dopedsilicon layer 604. The doping operation of the silicon layer beingformed concurrently with dopant gas introduction is called in-situdoping operation in the present disclosure. The cross sectional view atthe interfaces 605 a or 605 b enclosed by the dotted lines in FIG. 6Emay be substantially the same as those shown in FIG. 3G.

In an electronic circuit, the in-situ doping is applied to FinFETdevices that receive the input/output (I/O) power of the electroniccircuit. In some embodiments, the I/O devices receive greater powercompared to other devices in the electronic circuit. In someembodiments, the above-mentioned in-situ doping operation can be used tomanufacture the devices in the I/O region of an electronic circuit.

Now referring from FIGS. 6A-6D, 6F and 6G. The flows of forming thestructure of FIGS. 6A-6D have been discussed previously. For simplicity,the flows of forming the structure of FIGS. 6A-6D are not repeated againhere. In some embodiments, after the oxide material 603 is formed overthe fin structure 602 and the isolations 606, as shown in FIG. 6D, thesilicon layer 604 is then formed on the oxide material 603 as in FIG.6F. Subsequent to the formation of the silicon layer 604, the siliconlayer 604 is implanted with carbon and/or nitrogen at a concentration offrom about 5E19/cm³ to about 1E22/cm³ as shown in FIG. 6G. In someembodiments, the silicon layer 604 is annealed under a temperature offrom about 700 degrees Celsius to about 900 degrees Celsius for about 10to about 60 minutes. In some embodiments, the silicon layer 604 isannealed under an ambient of nitrogen. The implant operation of carbonand/or nitrogen is performed after the formation of the silicon layer604. Such operation is called ex-situ doping operation in the presentdisclosure.

FIG. 6H shows a cross sectional view of an ex-situ carbon-dopedpolysilicon gate after an anneal operation, in accordance with someembodiments of the present disclosure. The recrystallized grains of thecarbon-doped silicon are smaller than those of the conventionalnon-doped silicon layer. In some embodiments, the recrystallized grainsof the ex-situ carbon-doped silicon may be larger than those of thein-situ carbon-doped silicon layer.

In an electronic circuit, the ex-situ doping is applied to FinFETdevices that receive the input/output (I/O) power of the electroniccircuit. In some embodiments, the I/O devices receive greater powercompared to other devices in the electronic circuit. In someembodiments, the above-mentioned ex-situ doping operation can be used tomanufacture the devices in the I/O region of an electronic circuit.

Now referring to FIGS. 6A-6E, and FIG. 6G. In some embodiments, FIGS.6A-6E shows cross sectional views of forming an in-situ carbon-dopedsilicon layer in a FinFET structure. However, in some embodiments, thein-situ carbon-doped silicon layer is further ex-situ doped with carbonand/or nitrogen atoms, as shown in FIG. 6G, so as to reach a dopantconcentration of from about 5E19/cm³ to about 1E22/cm³. In an electroniccircuit, the in-situ doping, the ex-situ doping or a combination thereofcan be applied to form FinFET devices. In some embodiments, theabove-mentioned in-situ and ex-situ doping operation can be used tomanufacture the devices in the I/O region of an electronic circuit.

FIG. 7 represents the normalized poly grain size with respect to variousthermal anneal conditions. As the temperatures of the processesincrease, the normalized poly grain size increase. As the times whichthe processes take increase, the normalized poly grain sizes alsoincrease. Under an ex-situ nitrogen doping condition of 850 degreesCelsius for 40 minutes, a grain size of the ex-situ carbon-doped polysilicon layer is 75% of a grain size of a poly silicon layer withoutcarbon (e.g. a normalized grain size may decrease from about 2.1 toabout 1.6). The implant operation of carbon and/or nitrogen into thesilicon layer 604 can restrain the grains from recrystallization at theinterfaces 605 a and/or 605 b between the gate oxide 603 and the siliconlayer 604.

There may be two problems during the formation of the silicon layer 604in the FinFET structure. The first problem is that grains withorientation <111> may be formed. It is known that grains withorientation <111> have the lowest etching rate when etched by a wetetchant NH₄OH:H₂O (3.7 wt % of NH₄OH) under an etching temperature of 40degrees Celsius. After an etching operation of removing the grains atthe interfaces 605 a and/or 605 b, the <111> grains may not be removedcompletely. Referring back to FIGS. 4C and 4D, silicon grains 404 withorientation <111> are formed and the incomplete removal of the <111>grains can occur during the formation of the FinFET structure. Forexample, the operation of replacing a polysilicon gate with a metal gateinvolves an etching operation of the polysilicon layer. The <111> grainin the polysilicon layer may prevent the complete removal of thepolysilicon grains and result to a rough etching interface in proximityto the gate oxide. The interface between the subsequently formed metalgate and the gate oxide would not only be rough but also separated bythe unremoved polysilicon grains. Because the roughness of theinterfaces 605 a or 605 b between the gate oxide 603 and the metal gatemay lead to greater leakage current in the FinFET device with the metalgate, the performance of a FinFET device may be degraded. Therefore, ifthe polysilicon grain sizes are controlled to be smaller, the <111>grain is easier to be removed and thus less left-over polysilicon afterthe etching operation performed during gate replacement. To overcome theissue caused by the <111> grains at the interfaces 605 a and/or 605 bbetween the gate oxide 603 and the silicon layer 604, an in-situ and/orex-situ doping with carbon and/or nitrogen may be applied to decreasethe grain sizes.

In addition to the above-discussed impact of the roughness andincomplete removal of the polysilicon layer at the interfaces 605 aand/or 605 b between the gate oxide 603 and the silicon layer 604 of theFinFET device, the volume expansion of the grain growth duringrecrystallization at the interfaces 605 a and/or 605 b between the gateoxide 603 and the metal gate is also a yield killer for FinFET devicesbecause the roughness at the interfaces 605 a and/or 605 b is furtherenhanced as a result of the mechanical deformation.

Referring to FIG. 8A, a metal layer 804 is formed on a gate oxidematerial 803. FIG. 8A is a cross sectional view of a FinFET structure800 with a metal gate 804. The FinFET structure 800 includes a substrate801, a plurality of stripes 802 on the substrate 801, and a metal gate804 on a sidewall 802 b and a top surface 802 a of one of the pluralityof stripes 802. The isolations 805 are formed over the substrate 801.The FinFET structure further includes the oxide material 803 between themetal gate 804 and the plurality of stripes 802. The thickness of theoxide material 803 is from about 1 to about 4 nm.

Still referring to FIG. 8A, after removing the carbon-doped siliconlayer with an etching operation, grains at the interfaces 802 a and/or802 b between the silicon layer and the oxide material 803 may be nearlycompletely removed. A metal gate 804 is then formed on the oxidematerial 803. Thus the interfaces 802 a and/or 802 b between the metalgate 804 and the oxide material 803 do not include unremovedpolysilicon. In addition, a volume expansion of the silicon grainsduring recrystallization may cause the oxide material 803 to deform. Ametal gate 804 is then formed on the oxide material 803. The roughnessof the interface between the metal gate 804 and the oxide material 803may be carried to the final product of the FinFET structure 800. In someembodiments, the carbon-doped silicon layer undergoes lessrecrystallization growth and thus the volume expansion of the silicongrain is not as great as that in a silicon layer without carbon doping.As a result, the roughness at the interface between the metal gate 804and the oxide material 803 can be effectively reduced.

The metal gate 804 of the FinFET structure 800 may include multiplelayers. Referring to FIG. 8A, the metal gate 804 has a tri-layerstructure. The tri-layer structure includes a capping layer 804 a, adoping layer 804 b, and a conductive layer 804 c. The doping layer 804 bis configured to provide dopants, in some embodiments, aluminum ions, tothe conductive layer 804 c. The capping layer 804 a may include TiN, TaNor other materials. The capping layer 804 a is formed on top of thedoping layer 804 b. The capping layer 804 a is formed by variousdeposition techniques such as ALD, PVD, CVD, PECVD, or other suitabletechniques. In some embodiments, the capping layer 804 a is an optionallayer that can be removed from the tri-layer discussed herein. In FIG.8A, the metal gate 804 is conformally deposited on a top surface 802 aand a sidewall 802 b of one of a plurality of stripes 802. The pluralityof stripes 802 are separated by isolations 805.

FIG. 8B is a cross-sectional view illustrating in detail the FinFETstructure 800 of FIG. 8A, wherein the exemplary cross-sectional view isobtained by dissecting line C-C′ in FIG. 8A. FIG. 8B shows that a roughsurface is formed between the capping layer 804 a of the metal gate 804and the oxide material 803 under conventional manufacturing method for aFinFET structure, for example, the polysilicon gate is not doped withcarbon atoms. The volume expansion of grains during recrystallization atan interface 808 between the capping layer 804 a of the metal gate 804and the oxide material 803 may cause the interface 808 to be deformed.After an etching operation, recesses 806 in the oxide material 803 maybe formed. Subsequent to the etching operation, the capping layer 804 aof the metal gate 804 is formed on the rough surface of the oxidematerial 803. The capping layer 804 a may be formed in the recesses 806.In some embodiments, the protrusions 807 between the capping layer 804 aand the oxide material 803 can be the unremoved polysilicon grains. Therecesses 806 and protrusions 807 contribute to the average roughness atthe interface 808. Because the shape of the metal gate 804 isundesirably changed, the performance of the FinFET device isdeteriorated. In contrast, when using the in-situ doping and/or theex-situ doping as previously described in the present disclosure, therecrystallized grain size and the volume expansion can be reduced and asmoother interface between the metal gate 804 and the oxide material 803can be obtained. In some embodiments, the interface 808 between thecapping layer 804 a of the metal gate 804 and the oxide material 803 maynot include any unremoved polysilicon, that is, capping layer 804 a isin contact with the oxide materials 803 without being spaced by theunremoved polysilicon. In some embodiments, the average roughness of theinterface between the metal gate 804 and the oxide material 803 is in arange of from about 0.1 nm to 0.2 nm. As a result, the performance ofthe FinFET device can be improved.

In an electronic circuit, the in-situ doping, the ex-situ doping or acombination thereof may be applied to FinFET devices that receive theinput/output (I/O) power of the electronic circuit. In some embodiments,the I/O devices receive greater power compared to other devices in theelectronic circuit. In some embodiments, the above-mentioned in-situdoping, ex-situ doping or a combination thereof can be used tomanufacture the devices in the I/O region of an electronic circuit.

Some embodiments of the present disclosure provide a method of forming aFinFET. The method includes providing a substrate, forming a pluralityof stripes on the substrate, forming an oxide material over a topsurface and a sidewall of the one of the plurality of stripes, andforming a carbon-doped silicon layer over the oxide material at a firsttemperature. The method further includes elevating the temperature to asecond temperature greater than the first temperature, wherein theforming the carbon-doped silicon layer comprises an in-situ dopingoperation.

In some embodiments, the in-situ doping operation includes introducinggases comprising SiH₄, C₂H₄ or H₂.

In some embodiments, the first temperature is from about 450° C. toabout 650° C.

In some embodiments, the in-situ doping operation is conducted under apressure of from about 0.2 to about 5.0 torr.

In some embodiments, a concentration of the carbon-doped silicon layeris in a range of from about 5E19/cm³ to about 1E22/cm³.

In some embodiments, the second temperature is greater than about 700°C.

In some embodiments, the carbon-doped silicon layer comprises <111>polysilicon.

In some embodiments, an average grain size of the <111> poly silicon isbelow a predetermined value.

Some embodiments of the present disclosure provide a method of forming asemiconductor device. The method includes providing a substrate, forminga fin structure extruding from the substrate, forming shallow trenchisolations over the substrate, and forming an oxide material over thefin structure. The method further includes forming a carbon-dopedamorphous silicon layer or a carbon-doped poly silicon layer over theoxide material, wherein the forming a carbon-doped amorphous siliconlayer or a carbon-doped poly silicon layer comprises doping carbon in arange of from about 5E19/cm³ to about 1E22/cm³.

In some embodiments, the forming the carbon-doped silicon layer includesan in-situ doping operation, an ex-situ doping operation, orcombinations thereof.

In some embodiments, the ex-situ doping operation includes implantingthe amorphous silicon layer or the poly silicon layer with carbon andnitrogen.

In some embodiments, the in-situ doping operation comprises introducingone of SiH₄, C₂H₄ and H₂ when forming the carbon-doped amorphous siliconlayer or the carbon-doped poly silicon layer.

In some embodiments, the carbon-doped poly silicon layer is transformedfrom the carbon-doped amorphous silicon layer under a temperaturegreater than about 700 degrees Celsius.

In some embodiments, a grain size of the carbon-doped poly silicon layeris 75% of a grain size of a poly silicon layer without carbon.

In some embodiments, the carbon-doped poly silicon layer comprises grainorientation selected from <100>, <110> and <111>.

In some embodiments, the method comprises removing the carbon-dopedamorphous silicon layer or the carbon-doped poly silicon layer by anetching operation.

Some embodiments of the present disclosure provide a FinFET structure.The FinFET structure includes a substrate; a plurality of stripes on thesubstrate; a metal gate on a sidewall and a top surface of one of theplurality of stripes. The FinFET structure further includes an oxidematerial between the metal gate and the plurality of stripes, wherein anaverage roughness of an interface between the metal gate and the oxidematerial is in a range of from about 0.1 to 0.2 nm.

In some embodiments, the FinFET structure is in an I/O region of anelectronic circuit.

In some embodiments, thickness of the oxide material is from about 1.0nm to about 4.0 nm.

In some embodiments, the interface between the metal gate and the oxidematerial does not include polysilicon.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a FinFET, comprising:providing a substrate; forming a plurality of stripes on the substrate;forming an oxide material over a top surface and a sidewall of the oneof the plurality of stripes; forming a carbon-doped silicon layer overthe oxide material at a first temperature; and elevating the temperatureto a second temperature greater than the first temperature, wherein theforming the carbon-doped silicon layer comprises an in-situ dopingoperation.
 2. The method of claim 1, wherein the in-situ dopingoperation includes introducing gases comprising SiH₄, C₂H₄ or H₂.
 3. Themethod of claim 1, wherein the first temperature is from about 450° C.to about 650° C.
 4. The method of claim 1, wherein the in-situ dopingoperation is conducted under a pressure of from about 0.2 to about 5.0torr.
 5. The method of claim 1, wherein a concentration of thecarbon-doped silicon layer is in a range of from about 5E19/cm³ to about1E22/cm³.
 6. The method of claim 1, wherein the second temperature isgreater than about 700° C.
 7. The method of claim 1, wherein thecarbon-doped silicon layer comprises <111> polysilicon.
 8. The method ofclaim 7, wherein an average grain size of the <111> poly silicon isbelow a predetermined value.
 9. A method of forming a semiconductordevice, comprising: providing a substrate; forming a fin structureextruding from the substrate; forming shallow trench isolations over thesubstrate; forming an oxide material over the fin structure; forming acarbon-doped amorphous silicon layer or a carbon-doped poly siliconlayer over the oxide material, wherein the forming a carbon-dopedamorphous silicon layer or a carbon-doped poly silicon layer comprisesdoping carbon in a range of from about 5E19/cm³ to about 1E22/cm³. 10.The method of claim 9, wherein the forming the carbon-doped siliconlayer comprises an in-situ doping operation, an ex-situ dopingoperation, or combinations thereof.
 11. The method of claim 10, whereinthe ex-situ doping operation comprises implanting the amorphous siliconlayer or the poly silicon layer with carbon and nitrogen.
 12. The methodof claim 10, wherein the in-situ doping operation comprises introducingone of SiH₄, C₂H₄ and H₂ when forming the carbon-doped amorphous siliconlayer or the carbon-doped poly silicon layer.
 13. The method of claim 9,wherein the carbon-doped poly silicon layer is transformed from thecarbon-doped amorphous silicon layer under a temperature greater thanabout 700 degrees Celsius.
 14. The method of claim 9, wherein a grainsize of the carbon-doped poly silicon layer is about 75% of a grain sizeof a poly silicon layer without carbon.
 15. The method of claim 13,wherein the carbon-doped poly silicon layer comprises grain orientationselected from <100>, <110> and <111>.
 16. The method of claim 14,further comprising removing the carbon-doped amorphous silicon layer orthe carbon-doped poly silicon layer by an etching operation.
 17. Amethod of forming a FinFET, comprising: providing a substrate; forming astripe on the substrate; forming a dielectric layer; forming acarbon-doped silicon layer over the dielectric layer; annealing thecarbon-doped silicon layer; removing the annealed and carbon-dopedsilicon layer; and forming a metal layer over the dielectric layer. 18.The method of claim 17, comprising: introducing a gas, whereinintroducing the gas and forming the carbon-doped silicon layer over thedielectric layer are performed concurrently.
 19. The method of claim 18,wherein the gas includes SiH₄, C₂H₄ or H₂.
 20. The method of claim 17,wherein forming the carbon-doped silicon layer over the dielectric layercomprises: forming a silicon layer over the dielectric layer; andforming the carbon-doped silicon layer by doping carbon in the siliconlayer.